The present invention relates to an electromagnet drive device in which a movable body of a ferromagnetic material is operated at high speed by the electromagnetic force of a coil, and more precisely relates to an electromagnet drive device for controlling for example, an electromagnetic valve for accurately carrying out fuel injection in a diesel engine or electromagnetic shut off valve.
The present invention is provided with a storage coil for electromagnetic energy connected in association with an electromagnet to energize the electromagnet, the storage coil and a solenoid coil of the electromagnet being connected in series, and a portion of the electromagnetic energy stored in said storage coil is applied to the solenoid coil, and the time from a predetermined state for the solenoid coil to be energized is made shorter. Again for electromagnet deenergizing, the storage coil and the solenoid coil of the electromagnet are connected, and a portion of the electromagnetic energy produced by the solenoid coil is applied to the storage coil, and the time for the solenoid coil to be deenergized is shortened. Therefore, the electromagnet can be driven at high speed using a relatively low supply voltage.
FIG. 2 is a sectional view of a typical conventional electromagnet 1 implemented in accordance with the present invention. The electromagnet 1 has, as basic structural elements, a plunger 2 which is a movable body movable in an axial direction, a solenoid coil SC wound around the plunger 2, a first yoke 4 and a second yoke 5. The plunger 2 is formed of a ferromagnetic material and is fixed to a shaft 6. Toward one end of the shaft 6 (the left end in FIG. 2) is provided a bearing 7, and a guide body 8 is provided for the plunger 2. To one end of the shaft 6 is fixed one end of a return spring 9, and the other end of the return spring 9 is fixed in a fixed position. The right end of the plunger 2 in FIG. 2 is covered by a lid 10. When the solenoid coil SC is energized, the magnetic flux flows as shown by the indication .phi.1, a magnetic attraction is produced in the magnetic gap G between the second yoke 5 and the plunger 2, and the plunger 2 is thereby moved in the direction of the arrow W against the spring force of the spring 9. When the coil current is removed from the solenoid coil SC, the magnetic flux disappears, and the electromagnetic attraction is dissipated. The plunger 2 is therefore moved in the direction of the arrow Y by the spring force of the spring 9, and returns to the original state.
FIG. 11 is an electrical circuit diagram of an electromagnet drive device according to existing technology driving the electromagnet 1 shown in FIG. 2, and FIG. 12 is a timing chart explaining the operation of the electromagnet drive device.
Now with regard to the electrical circuit of FIG. 11, the operation will be explained with reference to the timing chart shown in FIG. 12. In FIG. 12, (1) shows the energizing command which commands whether or not the solenoid coil SC is to be energized, (2) shows the voltage waveform applied to the coil SC, and (3) shows the waveform of the current flowing through coil SC. Signal (4) shows the operating state of the transistor Q1, and (5) shows the operating state of the transistor Q2. As shown in (1), when the energizing command signal goes from low level to high level, as shown in (5) the transistor Q2 goes on, and also the timer circuit TM111 operates. As shown in (4), for the timer set time interval T1, the transistor Q1 is forcibly held on, and a current flows in the direction of the solid line arrow A1 in FIG. 11 from the direct current supply E through the transistor Q1, solenoid coil SC, transistor Q2 and current detecting resistor R1. The current Ie cannot, because of the inductance component Ls of the solenoid coil SC, increase instantaneously, but increases gently with time t. If the voltage of the direct current supply E is Ve, and the direct current resistance component of the solenoid coil SC is Rs, then the current Ie is given by the following expression (1). ##EQU1##
The time interval T1 of the timer circuit TM111 is set to slightly longer than the operating time of the plunger 2 of the electromagnet 1. When this time has elapsed, the output of the timer circuit TM111 returns to low level, and as shown in FIG. 12 (4) the solenoid coil SC is driven by the output of the comparator CM in chopper mode with the transistor Q1 undergoing repeated on/off operation at a rated current of the holding current level IH. In this rated current chopper mode, the current level Ie is detected by the current detecting resistor R1. When Ie grows larger than the holding current level IH, comparator CMP changes state, causing the transistor Q1 to go off. Then, the current Ie flows through the diode CR1 and in the direction of the broken line arrow A2 in FIG. 11 and decreases. When the current Ie has become less than the holding current level IH setting by the hysteresis amplitude .DELTA.I of the comparator, the transistor Q1 again goes on, and the current flows in the direction of the solid line arrow A1 in FIG. 11. Again the current Ie increases, and when it becomes larger than the holding current level IH setting, the operation of turning the transistor Q1 off is repeated. In other words, in the rated current chopper mode, by changing the time ratio of the on/off operation of the transistor Q1, the current Ie maintaining the attracting state of the electromagnet 1 is made equivalent to the holding current level IH, and is reduced from the current level when the plunger 2 is being moved obtained from the expression (1). Thus, the temperature increase of the solenoid coil SC is held back, and the current supply efficiency is increased.
As shown in FIG. 12 (1), when the energizing command signal goes from high level to low level the transistor Q2 goes off, and because of the back e.m.f. produced by the solenoid coil SC, the current flows in the direction of the dot-dash arrow A3 in FIG. 11 through the Zener diode ZD and diode CR2, and rapidly dissipates. At this point, if the Zener voltage of the Zener diode ZD is taken as VZ the current Ie is given by expression (2) as follows. ##EQU2##
A1so if the maximum surge voltage produced on the collector of transistor Q2 is VP, then this surge voltage VP is given by expression (3) as follows. EQU VP=VZ+Ve (3)
In other words, the maximum surge voltage VP corresponding to the sum of the maximum Zener voltage VZ and the supply voltage Ve is applied to the transistor switch Q2. Therefore when the solenoid coil SC is deenergized, the higher the Zener voltage VZ the faster it is deenergized, but also the higher the surge voltage VP.
In order to increase the speed of operation of the electromagnet, the electromagnetic attraction force when pulling the plunger 2 is required to be increased rapidly, but this electromagnetic attraction force is controlled by the current Ie flowing in the solenoid coil SC. Therefore, to move the plunger 2 rapidly, the current Ie flowing in the solenoid coil SC must be increased rapidly, and also when the plunger is returning, the current flowing in the solenoid coil SC must be decreased rapidly in order not to resist the return spring 9. As shown in expression (1) and expression (2), however, abrupt changes of the current Ie are limited by the inductance Ls of the solenoid coil SC, and speeding up of the movement of the plunger 2 is hampered. If when energizing the solenoid coil SC the supply voltage Ve is increased, or when deenergizing the Zener voltage VZ is increased, then it is possible to speed up the movement of the plunger 2. The result of this, however, is not only that the transistor switches Q1 and Q2 are required to sustain higher voltages, but also that since in the rated current chopper mode the switch on operation time is very short, high speed operation switch elements are required In order further to increase the suqply voltage Ve, it becomes necessary to construct the circuit from diodes and capacitors capable of withstanding high voltage. In practical implementation of devices, there are problems with impaired economy and reliability.
The object of the present invention is the provision of an electromagnet drive device capable of operating the electromagnet at high speed even if the power supply voltage is relatively low, and having high reliability.
According to the present invention, a storage coil for electromagnetic energy connected in association with an electromagnet is provided, for electromagnet energizing, the storage coil and a solenoid coil of the electromagnet are connected in series, and a portion of the electromagnetic energy stored in said storage coil is applied to the solenoid coil, and the time from a predetermined state for the solenoid coil to be energized is made shorter. Again for electromagnet deenergizing, the storage coil and the solenoid coil of the electromagnet are connected, and a portion of the electromagnetic energy produced by the solenoid coil is applied to the storage coil, and the time for the solenoid coil to be deenergized is shortened. Therefore, the electromagnet can be driven at high speed using a relatively low supply voltage.